1access(2) System Calls access(2)
2
6 access, faccessat - determine accessibility of a file
7
9 #include <unistd.h>
10 #include <sys/fcntl.h>
11 int access(const char *path, int amode);
13 int faccessat(int fd, const char *path, int amode, int flag);
16
19 The access() function checks the file named by the pathname pointed to
20 by the path argument for accessibility according to the bit pattern
21 contained in amode, using the real user ID in place of the effective
22 user ID and the real group ID in place of the effective group ID. This
23 allows a setuid process to verify that the user running it would have
24 had permission to access this file.
25 The value of amode is either the bitwise inclusive OR of the access
28 permissions to be checked (R_OK, W_OK, X_OK) or the existence test,
29 F_OK.
30 These constants are defined in <unistd.h> as follows:
33 R_OK Test for read permission.
35 W_OK Test for write permission.
38 X_OK Test for execute or search permission.
41 F_OK Check existence of file
44 See Intro(2) for additional information about "File Access Permission".
48 If any access permissions are to be checked, each will be checked indi‐
51 vidually, as described in Intro(2). If the process has appropriate
52 privileges, an implementation may indicate success for X_OK even if
53 none of the execute file permission bits are set.
54 The faccessat() function is equivalent to the access() function, except
57 in the case where path specifies a relative path. In this case the file
58 whose accessibility is to be determined is located relative to the
59 directory associated with the file descriptor fd instead of the current
60 working directory.
61 If faccessat() is passed in the fd parameter the special value
64 AT_FDCWD, defined in <fcntl.h>, the current working directory is used
65 and the behavior is identical to a call to access().
66 Values for flag are constructed by a bitwise-inclusive OR of flags from
69 the following list, defined in <fcntl.h>:
70 AT_EACCESS The checks for accessibility are performed using the
72 effective user and group IDs instead of the real user and
73 group ID as required in a call to access().
74
77 If the requested access is permitted, access() and faccessat()succeed
78 and return 0. Otherwise, −1 is returned and errno is set to indicate
79 the error.
80
82 The access() and faccessat() functions will fail if:
83 EACCES Permission bits of the file mode do not permit the
85 requested access, or search permission is denied on a
86 component of the path prefix.
87 EFAULT The path argument points to an illegal address.
90 EINTR A signal was caught during the access() function.
93 ELOOP Too many symbolic links were encountered in resolving
96 path, or loop exists in symbolic links encountered dur‐
97 ing resolution of the path argument.
98 ENAMETOOLONG The length of the path argument exceeds {PATH_MAX}, or
101 a pathname component is longer than {NAME_MAX} while
102 _POSIX_NO_TRUNC is in effect.
103 ENOENT A component of path does not name an existing file or
106 path is an empty string.
107 ENOLINK The path argument points to a remote machine and the
110 link to that machine is no longer active.
111 ENOTDIR A component of the path prefix is not a directory.
114 ENXIO The path argument points to a character or block device
117 special file and the corresponding device has been
118 retired by the fault management framework.
119 EROFS Write access is requested for a file on a read-only
122 file system.
123 The faccessat() function will fail if:
127 EBADF The path argument does not specify an absolute path and the fd
129 argument is neither AT_FDCWD nor a valid file descriptor open
130 for reading or searching.
131 The access() and faccessat() functions may fail if:
135 EINVAL The value of the amode argument is invalid.
137 ENAMETOOLONG Pathname resolution of a symbolic link produced an
140 intermediate result whose length exceeds {PATH_MAX}.
141 ETXTBSY Write access is requested for a pure procedure (shared
144 text) file that is being executed.
145 The faccessat() function may fail if:
149 EINVAL The value of the flag argument is not valid.
151 ENOTDIR The path argument is not an absolute path and fd is neither
154 AT_FDCWD nor a file descriptor associated with a directory.
155
158 Additional values of amode other than the set defined in the descrip‐
159 tion might be valid, for example, if a system has extended access con‐
160 trols.
161 The purpose of the faccessat() function is to enable the checking of
164 the accessibility of files in directories other than the current work‐
165 ing directory without exposure to race conditions. Any part of the path
166 of a file could be changed in parallel to a call to access(), resulting
167 in unspecified behavior. By opening a file descriptor for the target
168 directory and using the faccessat() function, it can be guaranteed that
169 the file tested for accessibility is located relative to the desired
170 directory.
171
173 See attributes(5) for descriptions of the following attributes:
174 ┌─────────────────────────────┬─────────────────────────────┐
179 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
180 ├─────────────────────────────┼─────────────────────────────┤
181 │Interface Stability │Committed │
182 ├─────────────────────────────┼─────────────────────────────┤
183 │MT-Level │Async-Signal-Safe │
184 ├─────────────────────────────┼─────────────────────────────┤
185 │Standard │See below. │
186 └─────────────────────────────┴─────────────────────────────┘
187 For access(), see standards(5).
190
192 Intro(2), chmod(2), stat(2), attributes(5), standards(5)
193SunOS 5.11 16 Jun 2009 access(2)